mAb could provide targeted approach to HLH treatment
Post-transplant follow-up is still early for most patients, but 2 patients have follow-up greater than 1 year. One child died of graft-vs-host disease around day 45, but the remaining patients who went on to HSCT are still alive.
Characteristics of response
For some patients, response to NI-0501 included a significant improvement in neutrophil count (8/10, P<0.001), platelet count (7/12, P<0.001), and ferritin level (P=0.0025). The median serum ferritin level was 4142 ng/mL at baseline and 1648 ng/mL at the end of treatment.
Both patients who were febrile at the start of treatment experienced rapid normalization of fever. Six of 7 patients with palpable spleen or liver at the start of treatment had an improvement in organomegaly. And 3 of 4 patients had resolution or improvement of CNS involvement.
Overall, there was a significant decrease in glucocorticoid dose. The median dose at baseline was 10.0 mg/m2. At the end of treatment, the median dose was 4.0 mg/m2 (P=0.023).
“One pharmacodynamic readout that’s useful for understanding IFNγ biology in vivo is CXCL9,” Dr Jordan noted. “This is secreted by mononuclear phagocytes in response to IFNγ. And most patients had a very clear fall in CXCL9 while receiving NI-0501.”
Adverse events and death
No off-target effects of NI-0501 have been observed, and none of the patients have withdrawn from the study for safety reasons.
There have been 14 serious adverse events in 8 patients, but only 1 of these events was considered treatment-related. The patient had necrotizing fasciitis following P aeruginosa skin infection, which resolved. This event was considered treatment-related by an investigator but not by the data monitoring committee or the sponsor.
In all, 3 patients have died, but none of the deaths were related to NI-0501. Two patients died of HLH/multi-organ failure, and 1 died of graft-vs-host disease.
Infections
“[NI-0501 provides] a targeted form of immune suppression, so we can expect that most concerns will be related to infection,” Dr Jordan said. “The effects of IFNγ on immune defense are actually predictable, and they’re predictable because of 2 patient populations.”
“First are the rare patients who are born with IFNγ-receptor deficiency, and second are individuals that develop neutralizing autoantibodies against IFNγ. Both patient populations experience infections with atypical mycobacteria, tuberculosis, Salmonella, and so forth.”
There were 10 infections already present at the start of the study—St epidermidis (n=1), C difficile (n=1), E coli (n=1, gram-positive), cytomegalovirus (n=1), Epstein-Barr virus (n=4), and parvovirus (n=1). All of these infections resolved with treatment.
Fourteen infections arose during the study course—St epidermidis (n=1), C difficile (n=1), P aeruginosa (n=1), K pneumoniae (n=1), E coli (1 gram-positive, 1 gram-negative), adenovirus (n=1), cytomegalovirus (n=2), Epstein-Barr virus (1 reactivation), parvovirus (1 reactivation), parainfluenza T3 (n=1), influenza A (n=1), and Candida (n=1).
Most of these infections resolved. The exceptions were the case of adenovirus, 1 case of cytomegalovirus (although there was improvement), the Epstein-Barr virus reactivation, the parvovirus reactivation (though improved), and the case of influenza A.
The researchers did not know if the parainfluenza T3 infection resolved. The patient’s viral status was not reassessed prior to death.
“So, in conclusion, NI-0501 has shown the potential to improve or resolve clinical and laboratory abnormalities of HLH, including CNS signs and symptoms,” Dr Jordan said. “The response to this agent appears to be independent of the underlying causative mutation. It’s also independent of the presence and type of infectious trigger.”
“NI-0501 was very well-tolerated. No safety concerns have emerged to date, and no infections known to be caused by deficiency of IFNγ have been observed. The neutralization of IFNγ by NI-0501 can offer an innovative and targeted approach to the management of HLH.” 
